Zastosowanie metody QuEChERS do analizy pozostałości pestycydów w pomidorach za pomocą GC-NPD/ECD

The Quick Easy Cheap Effective Rugged and Safe pesticide multiresidue method (QuEChERS) has been validated for extraction of two fungicides: azoxystrobin and chlorothalonil, which are frequently detected pesticides in Polish tomato samples. The homogenized samples (10 g) were spiked with a small volume of an appropriate standard mixture solution and shaken with acetonitrile (10 ml). As a slight modification, the obtained mixtures were frozen to save volatile pesticides before addition of salt mixture, consisting of anhydrous magnesium sulphate (4 g), sodium chloride (1 g), disodium hydrogen citrate sesquihydrate (0.5 g), and trisodium citrate dihydrate (1 g). After centrifugation an aliquot of the acetonitrile phase was transferred into a centrifugation tube containing a mixture of anhydrous magnesium sulphate and PSA sorbent (0.9 g). After purification with PSA, the extracts were re-acidified by adding 50 μL of the 5% formic acid solution. The extracts were transferred to the glass tubes and carefully evaporated to the dryness. The last step was adding acetone/hexane solution. A mixture of azoxystrobin and chlorothalonil, amenable to gas chromatography (GC), was quantitatively recovered from spiked tomato samples and determined using gas chromatography with nitrogen phosphorus detector and electron capture detector (GC–NPD/ECD). The spiking levels for the recovery experiments were: 0.02, 0.2 and 2.0 mg/kg for GC–NDP/ECD analyses. Mean recoveries mostly ranged between 70 and 120% (83.7% on average), relative standard deviations (RSD) were generally below 20% (9.8% on average). Based on the results, this methodology has been proven to be highly efficient and suitable for determination of azoxystrobin and chlorothalonil in tomato samples.